Kantronics KAM98 Repair

Discussion in 'Radio Circuits, Repair & Performance' started by WQ6N, Mar 24, 2018.

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  1. WQ6N

    WQ6N XML Subscriber QRZ Page

    I purchased a Kantronics KAM98 from the list here. I was doing good and had the unit up and running and exercising the modes. Approx two hours in, the TNC locked up and stopped communicating with the terminal
    Did a series of hard resets to no avail. Not even a bar indicator light. No RS232 control either and I tried a bunch of terminal programs. To be fair to the seller, he did say it powered on but no testing. So its on me to get it fixed.
    I started to change the CAPs on the board C99 10uF in the 5vdc regulator circuit first off. I have a solid 4.97vdc at the test points. But still no joy in bringing up the unit. Next I will change out C35 1uF and C61 47uF and that should take care of the polarized CAPs.
    Since my terminal programs are not talking to the TNC, I was thinking of changing out the RS232 Converter IC next [ADM208EANZ]. The non-Z are no longer available. I was also looking for a eprom v8.3 replacement in case mine was corrupt. Oh, I did validate all 26 Jumpers.
    Anyone with experience troubleshooting these units input would be welcome.
  2. N8YX

    N8YX Ham Member QRZ Page

    Does the microprocessor IC in that unit have a crystal-based reference oscillator?

    If so, is said oscillator working?

    If not, the unit won't bootstrap itself.
  3. W9GB

    W9GB Ham Member QRZ Page

    1.) The original Analog Devices part used lead (Pb) in its fabrication/tinning.
    2.) Restriction of Hazardous Substances Directive 2002/95/EC, (RoHS) short for Directive, restricted the use of certain hazardous substances in electrical and electronic equipment.
    It was adopted in February 2003 by European Union (and California), remainder of world followed.
    3.) Analog Devices created an RoHS compliant part (adding “Z” to part number) and obsoleted the leaded part.
    Assure that you have a CLEAN +5 VDC rail throughout the KAM-98.
    IF the previous owner lost the 7805 regulator (then replaced) — the voltage spike or regulation loss may have damaged other components or ICs (including the u-processor), even though it appeared functional.

    Kantronics KAM-98 Schematic Diagram (circa 1997 design)
    25-pin (DB-25) to 9-pin (DE-9) RS-232 adapter cables were common in 1980s (AT modem cables)
    The KAM-98 microprocessor is Motorola HC11 series, popular in 1990s with robotics systems.

    Bad handling can blow-out the TTL serial port (pins 72, 73) on the HC11.
    I have seen that problem with KPC-3+ (no ESD protection) installed as mobile devices in LMR usage.
    I have repaired three (3) surplus KPC-3+ units over past 10 years, that had this issue

    Analog Devices ADM208EAN — Datasheet
    24-pin PDIP, RS-232 with 15kV ESD protection

    Your Analog Device is ESD-tolerant, so unless you (or former owner) wired improperly —
    it should not stop due to static from changing connectors when powered (problem with earlier KPC-3 and 3+ TNCs)
    Last edited: Mar 26, 2018
  4. VE1IC

    VE1IC Ham Member QRZ Page

    With repairing TNC's, I always used my oscilloscope. Probe U2 and see if you see some ttl to serial conversion going on. If there is no TTL, I'd be checking the eeproms next.
  5. WQ6N

    WQ6N XML Subscriber QRZ Page

    Thank you very much with the pointers. I did change out all the polarized caps and U2. After completion is hooked the unit back up and gave it power. The tnc was in test/reset mode (J15) and it came up with good checks for the eprom and ram. I then put the test/reset jumper back into the off position and the device did respond properly. Pic attached. Then after aprox 10-15 min it quite working and no more command response. It appears that something took U2 out once again. Darn, had my fingers crossed. Time to take a look at the 5vdc rail across the board with a probe (especially B and C on U2). U1 and RLY1 locations are empty. Looking at the schematics there are dotted which may mean optional, don't know at this point. I did purchase 2ea U2 replacements but will want to ID the problem and not sacrifice the second one just to watch it go south. All - thank you so much for the assistance.
  6. WQ6N

    WQ6N XML Subscriber QRZ Page

    Bad handling can blow-out the TTL serial port (pins 72, 73) on the HC11.
    I have seen that problem with KPC-3+ (no ESD protection) installed as mobile devices in LMR usage.
    I have repaired three (3) surplus KPC-3+ units over past 10 years, that had this issue
    Just for the grins, I looked for the MC68HC11K0CFN4 online and saw some variants on ebay. long obsolete. Then I took a closer look at the solder joints. 6&7 top pins from the right looked like cold solder joints for sure. That is the top of the chip with the center indentation.
    There are 3ea .1uF caps C21, C22 and C37 that would have a impact on the 5vdc to U2. it will be interesting to see if one of them is shorted.

    Attached Files:

  7. VE1IC

    VE1IC Ham Member QRZ Page

    The thing to figure out here is:
    A: Does only the TTL / serial quit and the rest of the TNC keeps on working (like still be able to connect through the RF side to it).
    B: The CPU locks up and nothing works.
    If the CPU locks up for some reason and the TNC hung up, it has nothing to do with the TLL to serial converter IC. You could take the TTL to Serial converter IC out and hook up a little USB to TLL converter (those cheap ones from ali or ebay) and see what happens there. However, you need to figure out what really is happening with your TNC. So more testing is on order.
  8. WQ6N

    WQ6N XML Subscriber QRZ Page

    I believe there is something more than U2. Its locked up solid. No more time to spend on this and I am just going to write it off as a loss. 20 year old technology. Into the parts bin it goes.
  9. WQ6N

    WQ6N XML Subscriber QRZ Page

    Need a little help, I believe the Motorola MC68HC11K0CFN4 microcontroller might be bad. There are none available that I can find within reason. However, there is a enhanced version MC68HC11KA1CFN4 that is available within reason. I just don't know if the K series 0C and the KA series 1C are acceptable?

    Guess I am not quite ready to give up on this yet.
  10. W9GB

    W9GB Ham Member QRZ Page

    The part is from the MC68HC11 product family, 8-bit MPU.
    Freescale / Motorola made HUNDREDS of Varieties … to meet market needs 1980s-1990s.

    Read the Freescale (old Motorola) Data Sheets.

    Jameco Electronics (California) has carried this specific part, in the past.

    There are specialized electronics stores throughout Internet that stock old 1970-1990s ICs for vintage computer restorers.
    MANY in California !
    Example: Unicorn Electronics, near Pittsburgh, PA.

    I have been able to find some Motorola variants via Newark/Farnell.

    BIG LESSON … as these parts become harder to find …
    DOUBLE CHECK All DC Power Rails (Basic Electronics Repair 101).
    Last edited: May 18, 2018

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